In a semiconductor device including a semiconductor element bonded to a lead frame, an Ag layer may be selectively provided on the surface of the lead frame. For instance, in an integrated circuit device, the Ag layer can keep good contact with the bonding wire. Furthermore, in a light emitting device, an Ag layer having high light reflectance can be provided inside to increase the light extraction efficiency.
In the case of forming the Ag layer by plating, the unnecessary region of the surface can be masked with e.g. silicon rubber. Then, only the necessary region can be selectively plated. However, the plating liquid may leak to the side surface in the thickness direction of the lead frame. This is likely to form a side surface Ag layer, i.e., an Ag layer formed on the side surface of the lead frame. In particular, in the case of downsizing the semiconductor device, the lead frame is also downsized. This makes it more difficult to suppress the occurrence of the side surface Ag layer.
The side surface Ag layer formed by plating is likely to spread on the side surface along the longitudinal direction of the lead frame. The presence of the side surface Ag layer may induce peeling of the exterior plating layer made of e.g. SnAg. Another problem is that Ag causes migration along the gap between the lead frame and the resin molded body.